In recent years, imaging apparatuses (electrophotographic apparatuses), e.g., copying machines and printers, have been required to enhance the speed of image output and ensure high stability of output images in various use environments. For example, printers and the like, which have been previously used in offices in most cases, have been employed in severe high-temperature, high-humidity environments in recent years. Meanwhile, printers by using a one-component development system, which are suitable for miniaturization and enhancement of the speed, have increased because of demands for miniaturization and enhancement of the speed. In the one-component development system, there are few opportunities of contact between the toner and a member to charge the toner as compared with that in a two-component development system by using a carrier. Therefore, the amount of charge required for the toner has to be given by application of a relatively high stress. Consequently, it is necessary that the durability and the chargeability of the toner be improved in not only a common environment but also high-temperature, high-humidity environments.
PTL 1 describes a charge controlling agent having reduced hygroscopicity in a high-humidity environment.
However, it is difficult to make the charge controlling agent selectively present on the surfaces of the toner particles, so that the effect is not exerted easily and the density of an output image in a high-humidity environment may be reduced.
PTL 2 describes a toner obtained by aggregating and fusing resin particles, which are obtained by using a phase inversion emulsification method, on surfaces of core particles. In this case, resin particles are made to be selectively present on the outermost surfaces of toner particles easily.
However, the resin particles described in PTL 2 do not ensure sufficient charge stability in a high-humidity environment and the density of an output image in a high-humidity environment may be reduced.
Also, PTL 3 describes a toner, to which resin particles including a unit having a salicylic acid based substituent are allowed to adhere.
However, the resin particles described in PTL 3 have a broad particle size distribution and the durability may be poor.